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Audiometric and histological differences between the effects of continuous and impulsive noise exposures.

Hamernik-RP; Ahroon-WA; Hsueh-KD; Lei-F; Davis-RI
J Acoust Soc Am 1993 Apr; 93(4):2088-2095
Differences in acoustic trauma associated with impulsive and Gaussian noise exposure were studied in chinchillas. Chinchillas rendered monaural and instrumented with bipolar electrodes implanted in the inferior colliculus were exposed continuously for 5 days to 90 decibel (dB) sound pressure level (SPL) Gaussian noise, nonGaussian noise of moderate kurtosis, or pure impact noise. The frequencies of the three noise exposures ranged from 0.125 to 10.0 kilohertz (kHz). The peak intensity of the nonGaussian and impact noise was 114 and 117dB SPL, respectively, and the impulses were presented at the rate of four impacts per 820 milliseconds. Hearing thresholds were determined over the range 0.5 to 8KHz by measuring auditory evoked potentials at various times up to 30 days after the last exposure. Permanent threshold shifts (PTSs) were determined from the data. Thirty to 40 days after exposure ended the animals were killed and the cochleas were removed and examined by optical microscopy. Losses of sensory cells were determined. PTSs produced by the three types of noise exposure were similar for frequencies up to 2kHz. At higher frequencies, the PTSs diverged. The Gaussian noise produced the smallest PTSs and the pure impact noise the largest. The pattern of inner hair cell loss in the cochlea was similar for the three noise conditions except at 4.0kHz where the extent of loss in animals exposed to pure impact noise was significantly larger than the losses caused by the Gaussian and nonGaussian noise. The three noise types produced a similar pattern of outer hair cell loss except at 0.25kHz where the extent of loss induced by the pure impact noise was significantly greater than the losses produced by the other two noise types. The authors conclude that pure impact noise produces significantly larger PTSs than Gaussian noise at high test frequencies. The audiometric data do not agree with the magnitude and distribution of sensory cell loss, the most pronounced losses induced by pure impact noise occurring at very low frequencies.
NIOSH-Publication; NIOSH-Grant; Noise-induced-hearing-loss; In-vivo-studies; Laboratory-animals; Inner-ear; Histopathology; Hearing-threshold; Steady-state-noise; Impulse-noise; Acoustic-trauma
Communicative Disorders & Scis Research Foundation of Suny P O Box 9 Albany, N Y 12201
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Journal of the Acoustical Society of America
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State University of New York at Buffalo, Buffalo, New York